Probing migration of magnesium cations in spinel oxides

The top schemes depict the local cation arrangement in normal and inverted spinel oxides, with arrows highlighting the migration pathways of magnesium cations. The bar graph shows activation energies for ion migration in three different spinel oxides. The barriers were measured experimentally by both nuclear magnetic resonance (ssNMR) and muon spectroscopy (mSR), and compared with computational prediction using the nudge elastic band method

Scientific Achievement

Measurements of 25Mg variable temperature solid-state nuclear magnetic resonance (VT ss-NMR), and muon spin relaxation (μSR) in 3 spinel oxides reveal experimental magnesium hoping barriers as low as ∼0.6 eV, in agreement with independent density functional theory (DFT) predictions.

Significance and Impact

The measured barriers of magnesium cation migration are sufficiently low to support electrode function at reasonable particle sizes, challenging the existing notion that cation migration in oxides is the primary limiting factor hindering the development of functional, high-energy magnesium cathodes.

Research Details

  • Three spinel oxides containing Mg and either Mn or Cr were synthesized with high control of cation distribution in the structure.
  • The dynamics within the oxides, independently probed by NMR and mSR, are consistent with migration barriers for magnesium cations that are as low as 0.6 eV. The observed values are consistent with predictions by DFT.
  • Cation ordering led to the lowest migration barriers.
  • Deintercalation of magnesium was possible in the oxides with the lowest migration barriers.

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